This application claims priority from Japanese Patent Application 11-059981, filed Mar. 8, 1999 (MM/DD/YYYY), which is hereby incorporated by reference. The contents of the present application are not necessarily identical to the contents of the priority application.
1. Technical Field
The present invention relates to a disk drive which reads and writes data to a disk recording medium, and a retract circuit and a retract method for retracting a head by driving a head actuator when a power supply is turned off.
2. Description of the Related Art
A conventional disk drive comprises a magnetic-media disk which acts as a data recording medium, a spindle motor which rotates the disk, a head assembly, a voice coil motor (VCM), and a card assembly, in which an MPU, a spindle driver, a VCM driver, and a retract circuit are mounted. A head slider is mounted in the head assembly, and includes a magnetoresistive read head which reads data from and writes data to the disk. The VCM driver rotates the head assembly by driving the VCM when a drive power supply is turned on. The head assembly and VCM configure a head actuator.
While the disk drive is turned on, the disk drive drives the head actuator with the VCM driver, advances the head slider over a data area of a rotating disk surface, and reads data from and writes data to the data area of the disk. Hereinafter, this process of reading and writing data will be referred to as xe2x80x9cdisk operation.xe2x80x9d
In conventional systems, the head slider floats above the disk surface when the disk is rotating, but touches the disk surface when the disk stops rotation. If the head slider touches a data area surface, a problem such as scratching of the data area may happen, and hence the head slider is retracted from the data area when the disk stops rotation.
A load/unload mechanism and a CSS (contact/start/stop) mechanism are used for advancing a head slider over a data area of a disk and retracting the head slider from over the data area.
The load/unload mechanism retracts the head slider by loading the head assembly on a ramp near the disk assembly, by rotating the head assembly toward the ramp, in a process called xe2x80x9cloading.xe2x80x9d The mechanism also xe2x80x9cunloadsxe2x80x9d the head assembly by rotating the head assembly toward the disk, off the ramp, and over the data portion of the disk. When loading, the head assembly rises on a slope of the ramp to a parking surface by sliding a ramp surface in the unload direction. When unloading, the head assembly descends on the slope in the load direction, and goes over the disk surface from there.
In addition, the CSS mechanism retracts the head slider to a retract area provided on the disk surface. The head slider contacts a surface of the retract area when the disk stops the rotation, and floats from the surface of the retract area when the disk starts the rotation again.
The head slider is retracted by the VCM driver when the drive power supply is turned on, but the power of the VCM driver is also turned off when the drive power supply is turned off, and hence the retract circuit retracts the head slider.
Retract circuits are disclosed in, for example, U.S. Pat. No. 5,486,957 to Albrecht (hereinafter Albrecht) and U.S. Pat. No. 4,831,469 to Hanson, et al. (hereinafter Hanson).
A retract circuit according to Albrecht retracts the head slider by rectifying back-EMF (electromotive force) of the spindle motor and supplying current, derived from this rectified voltage, to a voice coil. The spindle motor continues to rotate due to inertia of the disk for the time being without immediately stopping the rotation when the drive power supply is turned off, and hence continues to generate the back-EMF after the drive power supply is turned off. In this retract circuit, as the back-EMF increases, the larger retract current supplied to the voice coil increases. As the torque constant becomes large, the back-EMF becomes large. Similarly, the larger the power supply voltage supplied to the spindle motor, and the greater the rotor radius is, the larger the torque constant of the spindle motor is.
In addition, a retract circuit according to Hanson charges the condenser with the power supply voltage when the drive power supply is turned on, and retracts the head slider by supplying the discharge current of the condenser to the voice coil when the drive power supply is turned off. In the retract circuit according to Hanson, as the power supply voltage and capacity of the condenser increase, the retract current supplied to the voice coil increases.
Nevertheless, in connection with thinning and miniaturization of a disk drive and the tendency toward a lower voltage of the drive power supply, it becomes difficult to unload a head assembly to a ramp in any one of the conventional retract circuits described above.
For example, in a disk drive whose disk diameter is nearly 1 inch and power supply voltage is 3.3 V, it is difficult to unload a head assembly onto a ramp by any one of the conventional retract circuits. Since the back-EMF of a spindle motor in the 1xe2x80x3 disk drive described above is small, i.e., nearly 1 V, it is not possible to secure sufficient retract current. In addition, since the capacity of a condenser which is sized for a 1xe2x80x3 disk drive miniaturized is insufficient, it is not possible to secure the sufficient retract current even if this type of condenser is charged with 3.3 V.
It is therefore one object of the present invention to provide an improved disk drive which reads and writes data to a disk recording medium.
It is yet another object of the present invention to provide an improved retract circuit for a disk drive system.
It is yet another object of the present invention to provide an improved method for retracting a head in a disk drive system.
The foregoing objects are achieved as is now described. The preferred embodiment provides a retract circuit and a retract method which comprises a booster circuit for boosting power supply voltage when power is applied, a condenser charged at the boosted voltage by the booster circuit at that time, and a control circuit for discharging the condenser to supply discharge current to a coil of a head actuator by when the power is cut off. According to the preferred embodiment, sufficient power is thereby reserved to completely retract the head when the power is disconnected.
When drive supply voltage Vcc is applied, a retract circuit charges a retract condenser Cr with boosted voltage Vup, equal to three times Vcc, generated by a booster circuit. Then, if the drive supply voltage Vcc is cut off and a VCM driver stops, the retract circuit detects power-off with a power OFF sense circuit, and provides retract delay time by a retract delay circuit. Furthermore, when the retract delay time elapses after the drive power supply is turned off, the retract driver switches the switching circuits on, discharges the retract condenser, charged at the boosted voltage, supplies discharge current to a voice coil, and retracts the head assembly.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.